Regulation of the air and fuel mixture supplied to an internal combustion engine, particularly an engine of the compression ignition type, has received widespread attention. Unless a satisfactory air/fuel ratio is achieved in the engine cylinders, engine operation will be adversely affected and fuel economy will be reduced. Moreover, accurate regulation of the air and fuel mixture will be necessary in order to achieve the stringent Environmental Protection Agency (EPA) emissions standards for the years 1991 and 1994. Proper regulation of the air/fuel mixture can eliminate or reduce substantially undesirable emission components from the engine exhaust. If air and fuel are supplied to the cylinders in a carefully controlled ratio which will allow complete combustion to occur under all operating conditions, expensive devices for removing exhaust emissions to achieve acceptable vehicle emission control may be entirely eliminated. In addition, efficient and economic engine operation will be realized as well.
Fuel systems for internal combustion engines wherein the fuel supplied to the engine is controlled in response to intake manifold pressure are well known. Many such systems include a source of fuel under pressure, e.g., a fuel pump, and a mechanism for regulating the pressure of the fuel supplied to an injector located at each cylinder. To achieve optimum air/fuel ratios under all operating conditions, highly sophisticated refinements have been made in these basic components to permit a carefully scheduled pressure output as a function of operator demand and engine speed. U.S. Pat. Nos. 4,187,817 and 4,248,188 to Wilson et al. are illustrative of such systems. The air/fuel control systems described in these patents mechanically modulate the flow of fuel into the engine in response to the pressure of the air in the intake manifold, which varies from a "no-air" condition below the rated pressure level to the full rated pressure. Both systems employ a diaphragm or flexible bellows operator for a fuel flow modulating valve responsive to engine intake manifold air pressure as sensed through an air line connecting the diaphragm operator with the intake manifold. The diaphragm is biased by a single spring selected and calibrated to provide modulation of the valve restriction to vary the fuel pressure in response to intake manifold pressure whereby the optimum air/fuel ratio can be maintained over a broad range of operating conditions. A drain line is additionally included in these systems to provide a fluid connection between the air fuel control mechanism and the engine fuel tank.
The air fuel control system disclosed in U.S. Pat. No. 4,187,817 further includes a flow restrictor in the air line to prevent engine fuel tank pressurization and reverse fuel flow into the engine's tank pressurization and reverse fuel flow into the engine's intake manifold in the event of a rupture of the diaphragm operator. The air fuel control system of U.S. Pat. No. 4,248,188 includes, in addition, an attenuator assembly which attenuates the transient response of the diaphragm operator by causing fuel to be supplied to a control chamber at a rate which is greater than that at which fuel is discharged from the chamber. While these air fuel control systems generally achieve an adequate air/fuel ratio, very precisely controlled metering of fuel is difficult to achieve and, hence, an optimum air/fuel ratio is not always realized for all engine operating conditions. Moreover, the variations in back pressure which have been characteristic of these prior art air fuel controls have caused air fuel control delay variations and, consequently, response problems. Further, engines intended for marine applications have not been able to employ the kind of drain line disclosed by the prior art air fuel controls. In the event of a diaphragm failure in a prior art air fuel control of the kind described in the aforementioned patents in a marine engine, fuel would tend to collect in the bilge.
Other air fuel control systems which employ diaphragm operators are also known in the prior art. For example, U.S. Pat. No. 3,795,233 to Crews et al. discloses a control device for a super-charged engine having a governor means connected to a fuel-adjusting member and a supercharger which supplies air to the engine through an intake manifold. Three spring members are employed in this system to balance forces on the diaphragm when there is no pressure in the control system chamber on the intake manifold side of the diaphragm. This system is responsive to both intake air pressure and engine oil pressure to override the governor means. However, the system described in this patent does not include a fuel flow modulating valve, but employs a mechanical linkage to vary the fuel supplied to the engine upstream of the throttle.
Moreover, none of the air fuel control devices disclosed by the prior art is completely tamper-resistant. Improper tampering with an internal combustion engine fuel supply adversely affects both fuel economy and long term engine durability. Fuel systems of the type described in the aforementioned patents generally include a drain line to the fuel tank for returning fuel which is not injected into the engine cylinders or which is bled from the gear pump section of the fuel pump and an adjustable air screw in the fuel pump. It is widely known that the short terms power output of engines equipped with such fuel system can be increased by clamping off this drain line and opening the air screw. However, the effects of such unauthorized modification can be extremely adverse, and may result in a reduction in fuel economy and shortened engine life. In addition, such unauthorized adjustments may cause engine emissions to vary from those achieved by the air fuel control settings set by the engine manufacturer so that the engine does not comply with emissions standards established by the EPA.
U.S. Pat. No. 4,869,219 issued to Brimmer et al. and assigned to the assignee of the present invention, the disclosure of which is incorporated herein by reference, discloses a dual spring air fuel control for PT fuel systems which overcomes a number of the shortcomings associated with the above noted prior art. Disclosed therein is a dual spring controlled air fuel control for a compression ignition type internal combustion engine, wherein fuel is supplied to the engine cylinders in response to the pressure of the air in the intake manifold. The stem valve, which includes a plunger and a barrel, operates to meter a controlled amount of fuel to the engine fuel supply system as the intake air pressure increases and reduces this metered flow as the intake air pressure decreases. Such is carried out by the cooperation of the plunger with the fuel input passage formed in the barrel. In one embodiment, this fuel input passage includes a large and small diameter inlet port which are connected to one another by a narrow channel such that when viewed from above the fuel inlet ports and the connecting channel assume a keyhole-like configuration. However, with this configuration, there is little viscosity sensitivity at no-air, there is no variation in the channel opening to account for increasing smoke, emissions, noise and response optimization, nor is there any region of the channel which provides for a uniform but quickly increasing bore diameter to provide driver feel once sufficient air is provided by the turbocharger to enable efficient combustion.
The prior art, therefore, fails to disclose an air fuel control for an internal combustion engine which responds quickly to meter a controlled, optimum amount of fuel in response to intake manifold air pressure, which is capable of controlling smoke, noise, emissions and provide transient engine response optimization during acceleration and which provides driver feel once sufficient air is provided by the turbocharger to enable efficient combustion.